Change in the Ultraviolet Spectrum of Solubilized Ca2+-Dependent ATPase from Sarcoplasmic Reticulum due to Binding with Ca2+Ions1

Abstract

Solubilized sarcoplasmic reticulum (SSR) was prepared by solubilizing fragmented sarcoplasmic reticulum (FSR) with a nonionic detergent (C₁₂E₈) then displacing the detergent with Tween 80, using a DEAE-cellulose column. The UV absorption of SSR decreased reversibly at about 286 and 292 nm on removal of free Ca²⁺ions, while no change in the fluorescence spectrum was detectable. On the other hand, the fluorescence intensity of FSR decreased 3–4% on removal of free Ca²⁺ions, as previously reported by Dupont [(1976) Biochem. Biophys. Res. Commun. 71, 544–550]. The UV absorption of FSR increased reversibly at about 270–280 nm on removal of free Ca²⁺ions, but the rate of the change was very slow (k=about 0.1 min⁻¹).